Performance Analysis of Regenerative Organic Rankine Cycle System for Solar Micro Combined Heat and Power Generation Applications

Abstract

The recurrent rises in energy demand and greenhouse gas emissions (GHGs) appeal for effective usage of energy sources. Micro-combined heat and power (micro-CHP) generation is regarded as an efficient replacement to traditional energy systems with distinct electrical and thermal production attributable to the greater energy effectiveness, reduced capacity and to the reduced GHGs. In this context, the Organic Rankine Cycle (ORC) is broadly recognised like a capable system to generate electrical power from solar energy, waste heat or low-quality thermal energy sources, even lower than $90^{\circ} C$. The present study aims at examining the performance of a solar driven micro-CHP system for residential buildings using a regenerative ORC. The analysis focuses on modelling, simulation and optimisation of various working fluids (WFs) in ORC to utilise low-temperature heat source from solar thermal collectors for heat and power generation. A detailed parametric study is performed to analyse the impacts of different WFs and operating situations at several temperatures of the hot and cold sources, as well as several temperatures and flow rates of the evaporator heating and condenser cooling WFs, on the system performance and heating and electrical power yields. The outcomes showed significant changes in performance such as efficiency and power extracted by the expander and generator based on the temperatures of each hot or cold sources for all WFs. The work extracted by the expander and the electrical power were within the range for residential building applications, in the range of 1–7 kWe, with an electrical isentropic efficiency of about 60% and cycle efficiency up to 9.8%, for a hot source temperature of $108 ^{\circ} C$. The WFs will operate in the hot source temperature range that would allow the use of a solar flat plate or evacuated tube collectors.